The invention provides a crankshaft assembling structure for a four-cylinder electric air compressor and a four-cylinder electric air compressor. According to the crankshaft assembling structure for the four-cylinder electric air compressor, a shaft hole is formed in the end face of a crankshaft driving end, at least one first key groove is formed in the inner wall of the shaft hole, and a bearingassembling base is arranged on the side face of the crankshaft driving end; an inner ring of a bearing is assembled on the bearing assembling base at the crankshaft driving end, and a balance block is assembled at the crankshaft driving end and is located on the outer side of the bearing; and a motor flange is assembled on and connected to the outer ring of the bearing, at least one second key groove is formed in an output shaft of a motor, the output shaft of the motor is inserted into the shaft hole in the crankshaft driving end, and the first key groove and the second key groove are connected through a key. The crankshaft assembling structure has the beneficial effects that a coupling connection way is replaced, arrangement of the electric air compressor is optimized, and assembling ofthe electric air compressor is simplified.